Process for preparing linear polyesters

ABSTRACT

A process for preparing linear polyesters by polycondensation of glycol terephthalates wherein (1) an antimony-containing catalyst which is soluble in the polycondensation system and (2) at least one member selected from Alpha -hydroxycarboxylic acids; Alpha , Beta -dicarboxylic acids; derivatives thereof such as ester, amide, acid anhydride, mixed acid anhydride or acid halide; and sulfur-containing derivatives thereof were added to the polycondensation system. Resultant polyesters exhibit excellent whiteness and transparency.

United States Patent [1 1 Chimura et al.

[ *Dec. 30, 1975 PROCESS FOR PREPARING LINEAR POLYESTERS [75] Inventors: Kazuya Chimura; Kazuo Ito;

Shunichi Takashima; Mizuo Shindo; Yoshihiro Shimoshinbara, all of Otake, Japan [73] Assignee: Mitsubishi Rayon C0,, Ltd., Japan Notice: The portion of the term of this patent subsequent to May 8, 1990,

has been disclaimed.

22 Filed: Oct. 19, 1973 21 Appl. No.2 407,987

Related U.S. Application Data [63] Continuation-in-part of Ser. No. 139,959, May 3,

1971, Pat. No. 3,822,239.

[30] Foreign Application Priority Data June 2, 1970 Japan.... 45-46918 June 3, 1970 Japan.... 45-47871 June 3, 1970 Japan.... 45-47872 June 9, 1970 Japan 45-49710 June 11, 1970 Japan 45-50613 June 11, 1970 Japan.... 45-50614 June 30, 1970 Japan.... 45-57029 Oct. 20, 1970 Japan.... 45-92294 Oct. 21, 1970 Japan 45-92642 Primary Examiner-Donald E. Czaja Assistant Examiner-W. C. Danison, Jr. Attorney, Agent, or FirmArmstrong, Nikaido & Wegner 57 ABSTRACT A process for preparing linear polyesters by polycondensation of. glycol terephthalates wherein (1) an antimony-containing, catalyst which is soluble in the polycondensation system and (2) at least one member selected from a-hydroxycarboxylic acids; a,B-dicarboxylic acids;lderivatives thereof such as ester, amide, acid anhydride, mixed acid anhydride or acid halide; and sulfur-containing derivatives thereof were added to the polycondensation system. Resultant polyesters exhibit excellent whiteness and transparency.

' *178 Glaims, No Drawings PROCESS FOR PREPARING LINEAR POLYESTERS This application is a continuation-in-part application to our copending application Ser. No. 139,959, filed on May 3, 1971, now US. Pat. No. 3,822,239.

The present invention relates to a process for preparing colorless linear polyesters and copolyesters by using an antimony-containing catalytic compound. More particularly, it relates to a process for' preparing linear polyesters and copolyesters having'improved whiteness and transparency, i.e. in which darkening or color formation inevitably caused by using only conventional catalytic antimony compounds are obviated, with an increased productivity by using a-hydroxycarboxylic acid; a,'B-dicarboxylic acid; a sulfur-containing derivative of the acid; or an ester, amide, acid anhydride, mixed acid anhydride or acid halide, of the acid or the sulfur-containing derivative, in addition to an antimony-containing catalyst.

Linear polyethylene terephthalate and copolyesters containing an ethylene terephthalate chain as a main component are particularly useful for textile fibers, film or molded articles. These polyesters are normally prepared through two reaction stages, that is, the first stage wherein, for example, dialkyl terephthalate is subjected to ester-interchange with ethylene glycol or terephthalic acid is directly esterified with ethylene glycol to be converted into bis-B-hydroxyethyl terephthalate or a low molecular weight polymer thereof and the second stage wherein the bis-B-hydroxyethyl terephthalate or its low molecular weight polymer is poly-condensed at high temperatures under reduced pressure to form a high molecular weight polyester. Selection of appropriate catalysts is essential to smoothly carry out both reactions in a reasonable time and to obtain a commercially valuable product. In other words, catalysts to be used have a great influence on not only productivity but also qualities of the resultant polymer such as whiteness, transparency, heat resistance, weathering resistance, stability at the time of processing and the like, as is well-known. Therefore, an elaborate consideration should be given to the selection of catalysts.

Referring to the second stage (polycondensation stage) catalysts, there are a number of known catalysts including various metallic and non-metallic compounds, among which, antimony compounds and germanium compounds are practically employed in the production of polyesters on the commercial scale. Antimony compounds have been used primarily because of their improved catalytic effect and low cost, but there is still a problem. That is, polyesters prepared by using conventional antimony compounds such as antimony trioxide are tinged with undesirable grey or greenish grey, which is 'due to the metallic antimony deposited by the reduction of the catalytic antimony compound during polycondensation, although. the polyesters are superior in heat resistance and stability at processing. The color formation is particularly important in the case where polyesters are to be used as textile fibers, films and'the like because it leads to a considerable reduction of transparency in the case of films and to a considerable reduction of whiteness in the case of textile fibers resulting in the deterioration of brilliancy in a dyeing process.

Thus, to avoid the problem, several new antimony catalysts have been heretofore proposed, including, for example, such pentavalent compounds as described in Japanese Pat. No. 10847/1961 and 6397/1964; pentavalent organoantimony compounds having the formula R SbO or R Sb(OH as described in Japanese Patent Publication 15999/1968; siloxyantimony compound having the formula (R R R SiO Sb[III], as described in Japanese Pat. No. 351/1970; and antimony salts of aliphatic mono-carboxylic acid having at least 12 carbon atoms, as described in British Pat. No. 1,168,149.

These antimony compounds, however, while being effective for minimizing or avoiding the color formation or darkening of polyesters, have some disadvantages; the pentavalent antimony compounds readily cause side reactions to form undesirable products such as diethylene glycol, which is vigorous in comparison with trivalent antimony compounds; the pentavalent organoantimony compounds and the siloxy-antimony compounds are too expensive because of organometallic compounds; and the antimony salts of aliphatic monocarboxylic acid having at least 12 carbon atoms exercise a slightly less effect for minimizing the color formation than the pentavalent antimony compound and should be used in great amounts in comparison with trivalent antimony compounds to ensure the reasonable rate of polycondensation. Accordingly, these antimony compounds are also unsatisfactory as cata lysts to be used in the manufacture of polyesters.

Fundamentally, in order to minimize the color formation or darkening of the polyesters, such antimony compounds wherein reduction potential thereof to metallic antimony can be maintained at a higher level during polycondensation than those of conventional trivalent antimony compounds, should be used. That is, antimony compounds to be used as a polycondensation catalyst should not have a tendency to be readily re-, duced in the polycondensation system. The abovementioned antimony compounds satisfy such a prerequisite.

Thus, to avoid the above-mentioned and other problems, a process for preparing improved linear polyesters and copolyesters, which are substantially colorless and have excellent whiteness and transparency and therefore, particularly useful for the preparation of films and textile fibers, has now been found.

The process of the invention is one for preparing linear polyesters or copolyesters which comprises condensing glycol terephthalate such as ethylene glycol terephthalate, 1,4-butanediol terephthalate and 1,4- cyclohexanedimethanol terephthalate, or a blend of the glycol terephthalate with minor amounts of at least one copolycondensation component such as phthalate, isophthalate, adipate, succinate and 4-B-oxyethoxybnzoate of glycol, e.g. ethylene glycol, 1,4-butane-diol or 1,4-cyclohexanediomethanol, in the presence of an antimony-containing polycondensation catalyst and at least one member selected from the group consisting of a-hydroxycarboxylic acid; a,B-dicarboxylic acid; a sulfur-containing derivative of a-hydroxycarboxyli'c acid or a,B-dicarboxylic acid, said derivative having been made by the substitution of at least one sulfur atom for at least one oxygen atom of the hydroxyl group or the carboxyl group of said acid; and ester, amide, acid anhydride, mixed acid anhydride or acid halide, of said acid or said sulfur-containing derivative; said member being present in such amounts that molar proportions 3 of antimony atom contained in said polycondensation catalyst to said member unit preferably range 1 0.5 to l 3.

The process of the invention produces polyesters or copolyesters possessing, by far, less darkness with a higher productivity in comparison with conventional processes wherein only a known antimony catalyst such as antimony trioxide and antimony acetate or the above-mentioned improved antimony catalysts such as pentavalent Sb compound is employed, i.e. without the compound of the present invention. These facts are surprising. The causes of the phenomena remaining unexplained are revealed, but it may be presumed that the phenomena are due to the fact that an antimonycontaining catalyst and a-hydroxycarboxylic acid, a,,B- dicarboxylic acid, a sulfur-containing derivative of the acid or a derivative thereof peculiary interact on each other in a polycondensation system and consequently, heat stability of the catalyst component is maintained at a considerably high level during polycondensation. For example, an antimony salt of monocarboxylic acid, e.g. antimony acetate, when it is heated in ethylene glycol, is readily subjected to glycolysis to produce a free carboxylic acid; the carboxyl group bonded to Sb atom disappear. On the other hand, for example, a solution prepared by the incorporation of malic acid into an-antimony trioxide solution in ethylene glycol, even after it is heated over a period of lhours at temperatures of 150 to 180C, exhibits strong absorption bands at 1725 cm and 1640 cm according to the infrared analysis, both absorptions being due to the asymmetric stretching vibration of COO group. Particularly, the latter absorption, which is due to a COO group directly bonded with an antimony atom, shows the possibility that the antimony catalyst has been changed into a compound having excellent stability against both heat and glycolysis, such as, for example by the addition of malic acid, and further, the stability is maintained all through the polycondensation.

. It may also be presumed that the high productivity of polyesters in the present invention is due to the fact that, as the antimony catalyst is transformed into such a stable compound as mentioned above, amounts of antimony to be reduced during the polycondensation are by far the least and consequently, an actually effective concentration of the antimony catalyst is considerably high.

The advantages obtainable in accordance with the invention cannot be enjoyed if instead of using the :x-hydroxycarboxylic acid or a,B-dicarboxylic acid a salt of such an acid with a metal, such as metals of IA, llA, [VA or VllB group of the Periodic Table (Merck index six edition) is used. The reasons for this, although not yet fully understood, are believed to be at least partially attributed to the fact that the metals of IA, llA, [VA or VllB group of Periodic Table have a metalic activity higher than an antimony atom. A salt of iuch a metal with a-hydroxycarboxylic acid or 01,13- :licarboxylic acid, when compared with the correrponding free acid, is more stable under the polycon- 4 densation conditions and is less likely to block and stabilize the antimony atom by reacting with the antimony-containing catalyst to form a compound, such as described above.

Gylcol terephthalates, which are to be condensed according to the present invention, may be prepared by the direct esterification of terephthalic acid with glycol or the ester-interchange of a lower dialkyl ester of terephthalic acid with glycol in a usual manner. Suitable glycols to be used for the esterification or the ester-interchange are those having 2 to 16 carbon atoms, which include, for example, ethylene glycol, l,4-butanediol, l,4-cyclohexanedimethanol and mixtures thereof. The esterification or ester-interchange of glycols, which is a precursory process of the polycondensation of the present invention, can be performed in normal manners in the presence of various known catalysts.

Glycol terephthalate to be condensed according to the present invention, may be used alone or as an admixture with each other or with minor amounts of copolycondensation component such as phthalic acid, isophthalic acid, adipic acid, succinic acid, 4-B-oxyethoxybenzoic acid, 1,4-butanediol, cyclohexane-l,4- dimethanol and the like.

Antimony-containing polycondensation catalysts to be used in the present invention include known catalysts, which are soluble in the polycondensation system; for example, antimony trioxide; antimony halide such as antimony chloride, antimony bromide and antimony fluoride; antimony sulfide; antimonic acid and metal salt thereof such as Ca antimonate, Mg antimonate, Zn antimonate, Mn antimonate, etc.; antimonous acid and metal salt thereof such as Ca antimonite, Mg antimonite, Zn antimonite, Mn antimonite, etc.; antimony glycoxide such as antimony ethylene glycoxide, antimony propylene glycoxide, antimony butylene glycoxide and the like; antimony phenoxide; antimony alkoxide such as antimony ethoxide, antimony methoxide, antimony propoxide, antimony butoxide and the like; and antimony carboxylate such as antimony acetate, antimony propionate, antimony butyrate, antimony formate, antimony benzoate, antimony toluylate and the like. Typical antimony compounds are antimony trioxide, antimony acetate, antimony ethoxide and antimony ethylene glycoxide.

a-hydroxycarboxylic acids, which are used together with an antimony-containing catalyst in the present invention, include those having 2 to 30 carbon atoms. But, those which have either a total of at least three hydroxyl and carboxyl groups or at least one aromatic ring in the a-position in relation to the carboxyl group, are particularly preferred in the present invention. Preferable a-hydroxycarboxylic acids include, for example, malic acid, citric acid, tartaric acid, gluconic acid, tartronic acid, methyltartronic acid, a-methylmalic acid, a-hydroxy-a'-methylsuccinic acid, ahydroxy-oz,a'-dimethylsuccinic acid, trimethylmalic acid, a-hydroxyglutaric acid, 4-hydroxypentane-l,3,4- tricarboxylic acid, glyceric acid, a,B-dihydroxyisobutyric acid, a-methyltartaric acid, a,B-dihydroxyglutaric acid, 2,3,4-trihydroxybutyric acid, dihydroxyfumaric acid, benzilic acid, a-phenyllactic acid and the like. Other a-hydroxycarboxylic acids having 2 to 30 carbon atoms such as glycollic acid, a-hydroxyisobutyric acid, a-hydroxyvaleric acid, a-hydroxylauric acid, a-hydroxystearic acid and the like, may also be used.

a,B-dicarboxylic acids, which are used together with an antimony-containing catalyst in the present invention, include those represented by the following formulae;

5 R,- coon R R, R COOH 2:c coon 2 c=c cooi-l wherein R R R and R are identical with or different R,, RQ/CCOOH 10 from each other and s'e lected fr'om a hydrogen atom and unsubstituted or substituted alkyl, cycloalkyl, aryl, -aralkyl, allyl and alkoxyl groups, said substituted R3 groups having a substituent selected from carbonyl group, halogen and carboxyl group; W, X, Y and Z are O=C COOH 94 15 identical with or different from each other and selected 1 R \-:ICCOOH from a hydrogen atom arid alkyl, hydroxyl and carboxy g groups; and n is an integer of at least R Such a,[3-dicarboxylic acids include, for example,

those represented by the formulae;

CH COOH CH HCOOH CH, HCOOH C, l-l -,CHCOOH CH CHCOOH H COOH, CH,.COOH, CH CHCOOH, C H CHCOOH. C H CHCOOH,

(CH;,) CCOOH -C H,,CHCOOH C H CHCOOH ,CH ECOOH I (CH COOH, (2H,COOH, (LH,COOH, H COOH.

C H CCOOH CH CCOOH CHCOOH I COOH CHCOOH, C,H COH, CH,CCOOH, OOH

CH3 COOH COOH COOH 5 COOH CH COOH, COOH I'l -COOH,

' COOH COOH C 5 COOH COOH COOH CH COOH COOH coon H00 COOH H0 coon H0O COOH. COOH,

COOH

Sulfur-containing derivatives of a-hydroxycarboxylic acid or a,B-dicarboxylic acid, which have been prepared by the substitution of at least one sulfur atom for at least one oxygen atom of the hydroxyl group or the carboxylic group of the a-hydroxycarboxylic acid or the a,B-dicarboxylic acid, are also used in addition to an antimony-containing polycondensation catalyst in the present invention.

Sulfur-containing derivatives of a-hydroxycarboxylic acid having been prepared by the substitution of at least one sulfur atom of the hydroxyl group or the carboxyl group of the acid include, for example, those represented by the formulae;

H; H, I HOCOCH, COOH, HOC H HCOOH, HOCOCH; H CHCOOH H IH IH HSCH, HCOOH. HSCH; H- H COOH, HOC HCOOH. I I L i Sulfur-containing derivatives of a,B-dicarboxylic acid, which have been prepared by the substitution of at least one sulfur atom for at least one oxygen atom of the carboxyl groups of the acid, include, for example,

those represented by the formulae;

HCOSH CH;,-CCOSH CH HOCOjH COSH HCOSH, CH-COSH, CH; COCH,

CH COSH,

COSH

HSCOCH HCOSH COSH.

HCOSH, CHCOSH,

(C Hs)(CH )ICOOCH CH OH, CH OCOCH,llHCOOCH OH OH OH (C H CONH (C H iCOOCOCH;,, CHaOCOCHziH-COOCOCHg,

C mi

HCOCl C H ZHCOCI,

ClCOiH-CHCOCI,

H H H CH OCOCH,IHCOOCH CH OH, HS-CH COOCH CH OH,

zSH

.exceed 3. The use of those compounds in excess of the Derivatives of a,B-dicarboxylic acid or sulfur-containing derivatives of the acid to be used in the present invention include, for example, those represented by the formulae;

CH-CO la-co it is to be understood that the compounds to be used together with an antimony-containing catalyst in the present invention is not limited to those exemplified above. It is also to be understood that those compounds may be in any type of both optical active and inactive.

Those compounds may be employed alone or as a mixture between them. The method of the incorporation of those compounds into the polycondensation system is not critical; they may be directly and separately added as they are or as solutions in glycol, or more preferably, they may be incorporated as a solution dissolved in an antimony catalyst solution in glycol, as mentioned hereinafter.

Used amounts of those compounds depend upon the used amounts of an antimony-containing catalyst. In order to achieve the greatest effect, that is, to obviate the color formation or darkening of the resulting polymers without deteriorating other qualities of same, those compounds are preferably used in such proportions that a molar ratio of those compounds to an antimony atom contained in the antimony catalyst does not I AH-COSCH CH,OCH HCOSC H above limit leads to a considerable reduction of heat stability and discoloration, e.g. yellowing, of the polymer. On the other hand, when a molar number of those compounds is less than that of the antimonyatom, the color formation or darkening of the polymer gradually increase with a decrease of the molar ratio. Particularly, when the molar ratio drops below one half, .the darkening is conspicuous. Therefore, a molar ratio of added to the reaction mixture at any stage from the time before the first stage esterification or ester-interchange commences to the time while the second stage polycondensation is going on, and in any form, i.e. as a solution in ethylene glycol, a slurry in ethylene glycol or a solid form. Preferably amounts of the catalytic antimony compound to be added to the reaction system are from 0.005 to 0.5% by weight, based on the weight of the resulting polyester.

In a most preferable embodiment of the present invention, both components of catalytic antimony compound and the above-listed compound are added in a form of solution or slurry in glycol such as ethylene glycol, propylene glycol and l,4-butanediol, particularly as a solution, which is prepared by dissolving the above-listed compound into a catalytic antimony compound (such as antimony trioxide and antimony ace-' tate) solution in ethylene glycol in such a proportion that a molar ratio of antimony atom contained in the catalytic antimony compound to the above-listed compound is l 1, to glycol terephthalate, produced by the esterification or ester-interchange, after the remaining esterification or ester-interchange catalyst is inactivated by the addition of phosphorus'compouri'ds, but before polycondensation commences. Then, the reaction mixture is polycondensed in usual manners.

Preferable phosphorus compounds to be added to inactivate the esterification or ester-interchange catalyst are lower alcohol esters of pentavalent phosphoric acid or reaction products of the esters and ethylene 1 '11 glycol. Trivalent phosphorus compounds are not preferable because these compounds have ahigh reducing power and therefore, in case they are present in the,

polycondensationsystem, reduce the antimony catalyst, which possibly leads to somedarkening of the resulting polyesters. The catalytic antimony compound of the present invention appears to exhibit a remarkably high reduction potential to metallic antimony in the polycondensation system in comparison with those of conventional catalytic antimony compounds such as antimony trioxide and antimony acetate and therefore, even in the case where trivalent phosphorus compounds are used together, it results in polyesters of less darkening than those from the conventional antimony catalysts. However, the darkening of polyesters obtained in the latter case is, of course, somewhat serious in comparison with that of the case where the pentavalent phosphorus compounds are used.

Further, in addition to the above-mentioned compound and the catalytic antimony compound, other polycondensation catalysts may be employed' in the present invention. The polycondensation catalysts include, for example, compounds containing zinc, silicone, germanium, cobalt, tin, lead, titanium and the like, among which germanium compounds and cobalt compounds are most preferable because their addition together with the antimony catalyst system of the present invention results in polyesters possessing excellent whiteness and transparency with high productivity.

Suitable germanium compounds include, for example, amorphous or crystal germanium dioxide, an eutectic mixture of crystal germanium dioxide and antimony trioxide, germanium glycoxide such as germanium ethylene glycoxide, germanium alkoxide and its derivatives such as germanium ethoxide, germanium carboxylate such as the acetate, germanium tetrahalide such as the tetrachloride and other known germanium compounds being readily and uniformly soluble in ethylene glycol or in the reaction mixture. These compoundsare preferably employed in the form of, for example, amorphous germanium dioxide, solid such as finely powdered crystal germanium dioxide ,having an average-particle size of no more than 3 an aqueous solution; an ethylene glycol solution being prepared by replacing the medium of ,an aqueous germanium solution or by directly dissolving germanium compounds in ethylene glycol in the presence of alkali metal salt or alkaline earth metal salt.

; Suitable cobalt compounds include, for example, carboxylic acid salts'such as cobalt formate, cobalt acetate, cobalt benzoate, cobaltstearate and the like; acethylacetonato cobalt, cobalt chloride, cobalt bromide, cobalt nitrate or cobalt sulfate. Amounts of these metal catalyst to be used in combination with the antimony catalyst of the present invention are not critical. Further, various additives such as stabilizer, pigment, delustrant and the like may be employed in the polycondensation.

. To sum .up, a method according to the present inventionproduces polyesters possessing, by far, less darkness in comparison with those of conventional method wherein known antimony catalysts, e.g. antimony trioxide and antimony acetate are used alone, with a high productivity.

. The invention will be further illustrated with reference to examples, in which parts and are both by weight unless otherwise specified and intrinsic viscosity [1 of polymers was determined in a mixture solvent of tetrachloroethane and phenol (l 1) at a temperature of 25C, and content of diethylene glycol (DEG) in polymers was determined by gas chromatography of hydrolyzed polymers.

Both luminous reflectance, represented by Y value, andexcitation purity, represented by Pl value, of polymers were determined as follows: The sample polymer was spun and drawn in a normal manner to form filaments having a fineness of d/ 36 fils. The filament test specimen was illuminated 'by a substantially unidirectional beam in an automatic recording spectrophotometer (manufactured by HITACHI SEISAKUSHO, Japan; Model EPR-2). Reflectance was measured on the test specimen and the magnesium oxide standard vwhite surface, the latter being used as a standard.

EXAMPLE 1 10,000 parts of dimethyl terephthalate and 7,500

parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate to effect ester-interchange while methanol, produced therefrom, was continuously distilled off from the reaction mixture. The reaction was completed three hours after its initiation. The reaction product was then distilled by heating to remove an excess of ethylene glycol therefrom.

A solution of 3.2 parts of trimethyl phosphate'in ethylene glycol was then added at a temperature of 240C to the reaction product, and followed by the addition of a catalytic antimony compound solution, which was prepared as follows; 4.6 parts of malic acid was added to a solution of 5 parts antimony trioxide dissolved in 200 parts of ethylene glycol by heating (a molar ratio of malic acid to Sb atom was 1/1 followed by agitation with the temperature being maintained at C for 5 hours. The reaction mixture was then vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mml-lg over a period of 2 hours. 7

The resultant polymer had a melting point of 261C and an intrinsic viscosity [1;] of 0.771. The polymer, was transparent with a very slightly yellow tinge but little or no darkening. Filaments, obtained therefrom by spinning and drawing, were characterized as having a Y value of 88.3% and a PI value of 98.9% and exhibiting excellent whiteness and luster.

CONTROL EXAMPLE I A process of Example 1 was repeated under the same conditions as those in Example 1 except that polycondensation was performed without adding malic acid.

The resultant polymer exhibited dark grey and a melting point of 260.5C and an intrinsic viscosity [-1 of 0.669, apparently showing that the polymer was by far inferior in the tone and the polycondensation rate was somewhat lower than that in Example 1. Filaments, obtained therefrom, were characterized as having a Y value of 78.3% and a PI value of 98.2% and exhibiting a considerably great darkness in comparison with those of Example 1.

EXAMPLE 2 A process of Example 1 was repeated under the same conditions as those in Example 1 except for added amounts of malic acid being 2.3 parts Le. a molar ratio of malic acid to Sb atom being 1/2, in place of 4.6 parts.

13 I The resultant polymer had a melting point of 261C and an intrinsic viscosity [7;] of 0.750, and had superior whiteness with little or no yellow tinge, but very slight darkening. Filaments, formed therefrom, were characterized as having a Y value of 86.6% and a P1 value of 99.4% and exhibiting excellent luster and whiteness.

EXAMPLE 3 A process of Example 1 was repeated under the same conditions as those in Example 1 except for added amounts of malic acid being 9.2 parts, i.e. a molar ratio of malic acid to Sb atom being 2/1, in place of 4.6 parts.

The resultant polymer had a melting point of 259.5C and an intrinsic viscosity [1;] of 0.736, and a slightly yellow tinge, but little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 85.6% and a PI value of 97.4% and being light with a slightly yellow tinge.

EXAMPLE 4 Using 7.2 parts of citric acid monohydrate (a molar ratio of citric acid to Sb atom was 1/1 in place of malic acid, a process of Example 1 was repeated with all other conditions remaininig the same.

The resultant polymer had a melting point of 260.5C and an intrinsic viscosity [1;] of 0.758 and was transparent with a slightly yellow tinge but little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 88.8% and a PI value of 98.2% and exhibiting excellent luster and white.

EXAMPLE 5 Using 3.6 parts of citric acid monohydrate (a molar ratio of citric acid to Sb atom was 1/2) in place of malic acid, a process of Example 1 was repeated with all other conditions remaining the same.

The resultant polymer had a melting point of 262C and an intrinsic viscosity [1 of 0.766 and excellent whiteness with little or no yellow tinge. Filaments, formed therefrom, were characterized as having a Y value of 89.2% and a PI value of 99.4% and exhibiting excellent luster and whiteness.

EXAMPLE 6 Using 2.57 parts of tartaric acid (a molar ratio of tartaric acid to Sb atom was 1/2) in place of malic acid, a process of Example 1 was repeated with all other conditions remaining the same.

The resultant polymer had a melting point of 260C and an intrinsic viscosity [1;] of 0.757 and excellent whiteness with a very slight yellow tinge. Filaments, formed therefrom, were characterized as having a Y value of 88.8% and a PI value of 99.1% and exhibiting excellent luster and whiteness.

EXAMPLE 7 9,000 parts of dimethyl terephthalate, 1,000 parts of dimethyl isophthalate and 7,500 parts of ethylene glycol were mixed and followed by the addition of 5 parts of calcium acetate at a temperature of 150C. The mixture was heated at temperatures of 150 to 220C over a period of 3 hours to perform ester-interchange. The reaction product was then distilled to remove an excess of ethylene glycol with the temperature being increased to 240C.

A solution of 2.3 parts trimethyl phosphate in ethylene glycol was then added to the reaction product, and followed by the addition of a catalytic antimony compound solution, prepared as follows; 2.76 parts of malic acid was added to a solution of 6.1 parts antimony acetate in 150 parts of ethylene glycol by heating (a molar ratio of malic acid to Sb atom was 1 1). The reaction mixture was vacuumed by degrees with the temperature being increased and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg over a period of two hours.

The resultant polymers had an intrinsic viscosity [1;] of 0.693 and excellent transparency and whiteness.

'Filaments, formed therefrom, were characterized as having a Y value of 90.4% and a PI value of 99.6%.

For purposes of comparison, the above polycondensation was repeated without adding malic acid. The resultant polymer was tinged with dark grey.

EXAMPLE 8 Using 10,000 parts of dimethyl terephthalate, 8,000 parts of ethylene glycol and 3 parts of manganese acetate, ester-interchange was repeated in the same manner as that of Example 1.

After the completion of ester-interchange, the reaction product was distilled to remove'an excess of ethylene glycol therefrom with the temperature being increased, and followed by the addition of a solution of 35 parts trimethyl phosphate in ethylene glycol. Then, a catalytic antimony compound solution, prepared as mentioned below, was added to the mixture.

The catalytic antimony compound solution was prepared as follows: 4 parts of antimony trioxide was dissolved in 200"parts of ethylene glycol by heating. To the solution, an a-hydroxyglutaric acid solution, which was prepared bydissolving 4 parts of the acid in parts of ethylene glycol at room temperature, was added (a molar-ratio of the acid to Sb atom was 1/1), and followed by the agitation at a temperature of C for 5 hours.

The reaction mixture containing the catalytic antimony compound solution was vacuumed by degrees with the temperature being gradually increased and finally, polycond'ensed at a temperature of 285C and a pressure of 2 mmHg over a period of two hours.

The resultant polymer had a melting point of 261 C and an intrinsic viscosity [1 of 0.767 and superior whiteness with little or no darkening. Filaments, formed therefrom were characterized as having a Y value of 88.8% and a PI value of 99.1% and exhibiting excellent whiteness and luster.

EXAMPLE 9 Using 2.9 paitsof glyceric acid (a molar ratio of glyceric acid toSb atom was 1 /1 in place of a-hydroxyglutaric acid, a process of Example 8 was repeated with all other cbnditions remaining the same.

The resultant polymer had a melting point of 260C and an intrinsic viscosity [1;] of 0.762 and exhibited little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 87.2% and a P1 value of 98.7% and exhibiting excellent luster and whiteness.

EXAMPLE 10 Using 4 parts of a-methylmalic acid (a molar ratio of oz-methylmalic acid to Sb atom was 1 /1) in place of a-hydroxyglutaric acid and further, adding a dispersion of 50 parts of titanium oxide in 200 parts of ethylene glycol to the reaction mixture after the completion of esterinterchange, a process of Example 8 was repeated with all other conditions remaining the same.

The resultant polymer had a melting point of 261 .5C and an intrinsic viscosity [1;] of 0.777 and superior whiteness. Filaments, formed therefrom, were characterized as having a Y value of 90.2% and a PI value of 99.1% and exhibiting excellent luster and whiteness.

EXAMPLE 1 l A mixture of 1,000 parts of terephthalic acid and 715 parts of ethylene glycol was charged into an autoclave with a distillation apparatus. The mixture was heated, while being stirred, under an atmosphere of nitrogen. When the pressure of the mixture reached 3 kg/cm with an increase of the temperature, a distilling valve was opened to remove water thus produced, and the esterification was performed at a temperature of 220C over a period of 3 hours with the removal of water.

On the other hand, a catalytic antimony compound solution was prepared as follows: 0.4 part of antimony trioxide was dissolved in parts of ethylene glycol by heating. To the solution, a malic acid solution, which was prepared by dissolving 0.37 part of the acid in 5 parts of ethylene glycol at a room temperature, was added and followed by the agitation at a temperature of 180C for 3 hours.

After the catalytic antimony compound solution was added to the reaction system, as mentioned above, the reaction system was vacuumed by degrees with the temperature being increased and finally, polycondensation was performed at a temperature of 285C and a pressure of 2 mmHg for 1.5 hours.

The resultant polymer had a melting point of 256C and an intrinsic viscosity [1;] of 0.712 and was light with a slightly yellow tinge but little or no darkening.

EXAMPLE 12 Using 7.8 parts of benzilic acid (a molar ratio of the acid to Sb atom was 1/1) in place of malic acid, a process of Example 1 was repeated with all other conditions remaining the same.

The resultant polymer had a melting point of 261C and an intrinsic viscosity [1;] of 0.774 and excellent whiteness with little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 88.1% and a PI value of 98.9% and exhibiting excellent luster and whiteness.

EXAMPLE 13 Using 10.3 parts of a-hydroxystearic acid (a molar ratio of the acid to Sb atom was 1/1) in place of malic acid, a process of Example 1 was repeated with all other conditions remaining the same.

The resultant polymer had a melting point of 260C and an intrinsic viscosity [1;] of 0.722 and an extremely light color but very slight darkening. Filaments, formed therefrom, were characterized as having a Y value of 85.2% and a PI value of 98.7%.

EXAMPLE 14 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate to perform ester-interchange while methanol, produced therefrom, was continuously distilled off from the reaction mixture. Ester-interchange was completed three hours after its initiation. An excess of ethylene glycol was 16 then distilled off from the reaction product with the temperature being increased.

To the reaction product, a solution was added at a temperature of 240C, which solution was prepared by reacting 3 .2 parts of trimethyl phosphate with parts of ethylene glycol at a temperature of 175C, while methanol, thus produced, was distilled off from the reaction mixture. Then, a catalytic antimony compound solution, prepared as mentioned below, and a solution of 0.2 parts amorphous germanium dioxide in 20 parts of ethylene glycol were added to the reaction mixture. The reaction mixture was vacuumed by degrees and finally, polycondensed at a temperature of 280C and a pressure of 2 mmHg over a period of two hours.

The catalytic antimony compound solution was prepared as follows: A solution of 3.7 parts malic acid dissolved in 50 parts of ethylene glycol at room temperature was added to a solution of 4 parts of antimony trioxide in 150 parts of ethylene glycol (a molar ratio of malic acid to Sb atom was 1/1) and followed by the agitation over a period of 5 hours with the temperature being maintained at C.

The resultant polymer had an intrinsic viscosity [17] of 0.776 and DEG of 0.61% and was colorless, transparent. Filaments, obtained therefrom, were characterized as having a Y value of 91.3% and a PI value of 99.7% and exhibiting excellent luster and whiteness.

EXAMPLE 15 Without adding amorphous germanium dioxide, a process of Example 14 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.744 and DEG of 0.60% and was tinged slightly yellow but little or no dark. Filaments, formed therfrom, were characterized as having a Y value of 87.8% and a PI value of 98.4% and a slightly yellow tinge in comparison with those in Example 14.

EXAMPLE 16 Using 2.9 parts of citric acid monohydrate (a molar ratio of citric acid to Sb atom was 1/2) in place of malic acid, a process of Example 14 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.784 and DEG of 0.59% and was colorless and transparent. Filaments, formed therefrom, were characterized as having a Y value of 90.9% and a P1 value of 99.6% and exhibiting excellent whiteness and luster.

EXAMPLE 17 Using 5.8 parts of citric acid (a molar ratio of the acid to Sb atom was 1/1 in place of malic acid, a process of Example 14 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.769 and DEG of 0.60% and was colorless, transparent. Filaments, formed therefrom, were characterized as having a Y value of 91.2% and a PI value of 99.6% and exhibiting excellent luster and whiteness.

EXAMPLE 18 Using 2 parts of tartaric acid (a molar ratio of the acid to Sb atom was H2) in place of malic acid, a process of Example 14 was repeated with all other conditions remaining the same.

= 150 to 220C under an 17 The resultant polymer had an intrinsic viscosity [1 of 0.766 and DEG of 0.58% and was colorless and transparent. Filaments, formed therefrom, were characterized as having a Y value of 90.3% and a P1 value of 99.3% and exhibiting excellent luster and whiteness.

EXAMPLES 19-21 Without adding amorphous germanium dioxide, processes of Examples 16-18 were repeated with all other conditions remaining the same. Characteristics of the resultant polymers and filaments are shown in Table 1.

Using a solution, which was prepared by dissolving 0.2 part of commercially available crystal germanium dioxide in 20 parts of ethylene glycol in the presence of 0.17 part of calcium acetate while being heated with agitation over a period of 3 hours, in place of an amorphous germanium dioxide, solution a process of Example 16 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1 of 0.792 and DEG of 0.59% and was colorless and transparent. Filaments, formed therfrom, were characterized as having a Y value of 90.7% and a P1 value of 99.5% and exhibiting excellent whiteness and luster.

EXAMPLE 23 Using a 0.5% germanium dioxide solution in ethylene glycol, which was prepared by dissolving 0.2 part of commercially available crystal germanium dioxide in 40 parts of water at a temperature of 100C and then, adding 50 parts of ethylene glycol to the solution and heating the resulting mixture to distill off water together with minor amounts of ethylene glycol from the mixture, in place of an amorphous germanium dioxide solution, a process of Example 16 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.772 and DEG of 0.58%. Filaments, formed therefrom, were characterized as having a Y value of 90.8% and a PI value of 99.6% and exhibiting excellent whiteness and luster.

EXAMPLE 24 EXAMPLE 2s 10,000 parts of dimethyl terephthalate ancl 7,500 parts of ethylene glycol were heated at temperatures of atmosphere of nitrogen'for 3 hours in the presence of 7 parts of calcium acetate to perform esterinterchange. Then an excess of ethylene glycol was distilled off from the reaction productwith the temperature being increased. Thereafter, a solution, which was prepared by treating 3.3 parts of trimethyl phosphate with parts of ethylene glycol at a temperature of 170C, was added to the reaction product, further followed by the addition of a catalytic antimony compoundsolution.

The catalytic antimony compound solution was prepared as follows: 4 parts of antimony trioxide and 0.3 part of crystal germanium dioxide fine powder having an average diameter of 2.4 p. were simultaneously dissolved in 200 parts of ethylene glycol by heating. Then, a malic acid solution, prepared by dissolving 3.7 parts of malic acid (a molar ratio of the acid to Sb atom was 1/ 1) in 50 ml of ethylene glycol at room temperature, was added to the solution and followed by the agitation at a temperature of C for 5 hours. I

Then, the above reaction mixture was vacuumed by degrees and finally, polycondensed at a temperature of 280C and a pressure of 2 mmHg over a period of 2 hours.

The resultant polymer had an intrinsic viscosity [1;] of 0.788 and DEG of 0.61% and was extremely white. Filaments, formed therefrom, were characterized as having a Y value of 90.6% and a PI value of 99.6% and exhibiting excellent luster and whiteness.

For comparison pruposes, the above process was repeated in the same conditions as those mentioned above except for the absence of the crystal germanium dioxide fine powder. The resultant polymer had an intrinsic viscosity [1 of 0.740 and DEG of 0.60%. Filaments, formed therefrom, were characterized as having a Y value of 87.1% and a PI value of 98.4% and a very slightly yellow tinge.

EXAMPLE 26 Using 0.7 part of germanium tetraethoxide in place of crystal germanium dioxide fine powder, a process of Example 25 was repeated with all other conditions remaining the same.

The resulting polymer had an intrinsic viscosity {1;} of 0.779 and DEG of 0.62%. Filaments, formed therefrom, were characterized as having a Y value of 91.0% and a PI value of 99.5% and excellent luster and whiteness.

EXAMPLE 27 To an ester-interchange reaction product beingthe same as that obtained in Example 16, a solution, which was prepared by treating 3.2 parts of trimethyl phosphate with 100 parts of ethylene glycol at a temperature of C, was added and followed by the addition of a catalytic antimony compound solution, prepared as mentioned below, and a solution of 2 parts amorphous germanium dioxide in 100 parts of ethylene glycol.

The catalytic antimony compound solution was prepared as follows: A solution of 2.8 parts malic acid (a molar ratio of the acid to Sb atom was l/ l dissolved in 50 parts of ethylene glycol at a room temperature was added to a solution of 6 parts antimony acetate (Sb content of which corresponds to 3 parts of antimony trioxide) in 150 parts of ethylene glycol and followed by the agitation over a period of 5 hours with the temperature being maintained at 120C.

The above reaction mixture was vacuumed by de- CONTROL EXAMPLE 2 Using only 2 parts of amorphous germanium dioxide as a polycondensation catalyst, i.e. without using antimony acetate and malic acid, a process of Example 27 was repeated with all other conditions remaining the same. The resultant polymer had an intrinsic viscosity [1 of 0.609 and. DEG of 1.22%, showing that the side reaction to produce diethylene glycol was not suppressed in comparison with the case of an antimony compound and malic acid being used. Filaments, formed therefrom, were characterized as having a Y value of 91.5% and a PI value of 99.6% and exhibiting excellent luster and whiteness.

EXAMPLE 28 A mixture of 9,000 parts of dimethyl terephthalate, 1,000 parts ofdimethyl isophthalate and 7,500 parts of ethylene glycol, after parts of calcium acetate being added to the mixture at a temperature of 150C,- was heated at temperatures of 150 to 220C over a period of 3 hours to perform ester-interchange. An excess of ethyleneglycol was distilled off from the reaction productwith the temperature being increased. Then, a solution was added to the above reaction product, which solution was prepared by heating a mixture of 4.6 parts of trimethyl phosphate and 100 parts of ethylene glycol at a temperature of 170C while methanol, produced therefrom, was distilled off from the reaction mixture, followed by the addition of a catalytic antimony compound solution, prepared as mentioned below, and 0.5 partof amorphous germanium dioxide. The resultant mixture was vacuumed by degrees with the temperature being gradually increased and finally, polycondensed at atemperature of 285C and a pressure of 2 mmHg for 1.5 hours.

The catalytic antimony compound solution was prepared as follows: 5.8 parts of citric acid (a molar ratio of the acid to Sb atom was III) was added to a solution of 7 parts antimony triethoxide (Sb content of which corresponds to 4 parts of antimony trioxide) and followed by the agitation over a period of 5 hours with the temperature being maintained at 150C.

The resultant polymer had an intrinsic viscosity [1 of 0.718 and DEG of 0.63% and was colorless, transparent. Filaments, formed therefrom, were characterized as having a Y value of 90.8% and a PI value of 99.5% and exhibiting excellent luster and whiteness.

1n the case where the above polycondensation was performed in the absence of only amorphous germanium dioxide for comparison purposes, the resultant polymer had an intrinsic viscosity [1;] of 0.626 and DEG of 0.60%. Filaments, formed therefrom, were characterized as having a Y value of 87.2% and a PI value of 98.4% and a very slight yellow tinge.

EXAMPLE 29 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate, while methanol, produced therefrom, was continuously distilled from the reaction mixture, to perform ester-interchange. The reaction was completed 3 hours after its initiation. After an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased, a solution was added to the above reaction product, which solution was prepared by treating 3.2 parts of trimethyl phosphate with parts of ethylene glycol at a temperature of 175C while methanol, produced therefrom, was distilled from the reaction mixture. Further, a catalytic antimony compound solution prepared as mentioned below, was added to the reaction product. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 280C and a pressure of 2 mml-lg for 2 hours.

The catalytic antimony compound solution was prepared as follows: 4.2 parts of an eutectic mixture, prepared from 8 parts of antimony trioxide and 0.4 part of germanium dioxide, was dissolved in 150 parts of ethylene glycol. Then, a solution of 3 parts malic acid (a molar ratio of the acid to Sb atom was 0.8/1 dissolved in 50 parts of ethylene glycol at room temperature was added to the solution followed by agitation for 5 hours with the temperature being maintained at C.

The resultant polymer had an intrinsic viscosity [1 of 0.771 and DEG of 0.62% and was colorless and transparent. Filaments, formed therefrom, were characterized as having a Y value of 90.3% and a PI value of 99.4% and exhibiting excellent luster and whiteness.

EXAMPLE 30 Using 4.2 parts of antimony trioxide in place of the eutectic mixture in Example 29, a process of Example 29 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1 of 0.724 and DEG of 0.60% and was tinged slightly yellow but with little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 86.8% and a P1 value of 98.4% and a slightly yellow tinge in comparison with those in Example 29.

EXAMPLE 31 10,000 parts of dimethyl terephthalate and 7,5 00 parts of ethylene glycol were heated at temperatures of to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate, while methanol, thus produced therefrom, was continuously distilled off from the reaction mixture, to perform esterinterchange. The reaction was completed 3 hours after its initiation. Then, an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased. A solution of 3.2 parts trimethyl phosphate in ethylene glycol was then added to the reaction product at a temperature of 240C followed by the addition of a catalytic antimony compound solution, prepared as mentioned below. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mml-lg for 2 'hours.

The catalytic antimony compound solution was prepared by adding 5 parts of dimethylmaleic acid (a molar ratio of the acid to Sb atom was 1 1 to a solution of 5 parts antimony-trioxide in 200 parts of ethylene glycol and then stirring the mixture for 5 hours with the 21 temperature being maintained at 120C.

The resultant polymer had an intrinsic viscosity [1 of 0.766 and a melting point of 262C and exhibited excellent luster and was extremely light with a very slightly yellow tinge but little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 88.7% and a PI value of 98.6% and exhibiting excellent luster and whiteness.

EXAMPLE 32 A process of Example 31 was repeated under the same conditions as those in Example 31 except for added amounts of dimethylmaleic acid being 2.5 parts (a molar ratio of the acid to Sb atom was 1/2) in place of parts.

The resultant polymer had an intrinsic viscosity [1 of 0.742 and a melting point of 261C and exhibited superior whiteness with little or no yellow tinge. Filaments, formed therefrom, where characterized as having a Y value of 87.0% and a P1 value of 98.8% and excellent luster and whiteness.

EXAMPLE 33 A process of Example 31 was repeated under the same conditions as those in Example 31 except for added amounts of dimethylmaleic acid being parts (a molar ratio of the acid to Sb atom was 2/1) in place of 5 parts.

The resultant polymer had an intrinsic viscosity [1;] of 0.762 and a melting point of 260C and was tinged slightly yellow but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 88.1% and a P1 value of 97.8% and exhibiting excellent lightness and luster.

CONTROL EXAMPLE 3 A process of Example 31 was repeated under the same conditions as those in Example 31 except for added amounts of dimethylmaleic acid being 25 parts (a molar ratio of the acid to Sb atom was 5/1 in place of 5 parts.

The resultant polymer had an intrinsic viscosity [1 of 0.758 and a melting point of 259C and was tinged with little or no darkening but was considerably yellow. Filaments, formed therefrom, were characterized as having a Y value of 85.1% and a PI value of 96.2% and being light and lustrous with a considerably yellow tinge.

- EXAMPLE 34 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of magnesium acetate, while methanol, produced therefrom, was continuously distilled off from the reaction mixture, to perform ester-interchange. The reaction was completed 3 hours after its initiation. Then, an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased. A solution of 3.2 parts trimethyl phosphate in ethylene glycol was then added to the reaction product at a temperature of 240C followed by the addition of a catalytic antimony compound solution, prepared as mentioned below. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg for 2 hours.

The catalytic antimony compound solution was pre-' pared by adding 4 parts of maleic acid (a molar ratio of 22 the acid to Sb atom was l/l) to a solution of 5 parts antimony trioxide dissolved in 200 parts of ethylene glycol by heating and then stirring the mixture for 5 hours with the temperature being maintained at C. The resultant polymer had an intrinsic viscosity [1 of 0.767 and melting point of 260C and exhibited excellent luster' and was extremely light with a very slight yellow tinge but little or no darkening. Filaments, formed therefrom, were characterized as having a Y value of 87.7%and a PI value of 98.7% and exhibiting excellent luster and whiteness.

EXAMPLE 35 A process of Example 34 was repeated under the same conditions as those in Example 34 except for added amounts of maleic acid being 8 parts (a molar ratio of the acid to Sb atom was 2/1) in place of 4 parts.

The resultant polymer had an intrinsic viscosity [1;] of 0.756 anda melting point of 260C and was tinged slightly yellow but with little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 85.8% and a PI value of 97.7% and exhibiting extreme lightness with a slightly yellow tinge.

EXAMPLE 36 Using 10.3 parts of antimony acetate (Sb content of which corresponds to 5 parts of Sb O and a molar ratio of maleic acid...to Sb atom is III) in place of antimony trioxide, a process of Example 34 was repeated with all other condition's remaining the same.

The resultant polymer had an intrinsic viscosity [1 of 0.778 andia'melting point of 260.5C and was transparent with a slightly yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y'value of 88.1% and a PI value of 98.6%.

. EXAMPLE 37 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene "glycol were heated at temperatures of to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate, while methanol, producedtherefrom, was continuously distilled off from the mixture', to perform ester interchange. The reaction was completed 3 hours after its initiation. Then, an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased. A solution of 3.2 parts trimethyl phosphate in ethylene glycol was then added to the reaction product at a temperature of 240C and followed by the addition of a catalytic antimony compound solution, prepared as follows: 4 parts of fumaric acid (a molar ratio of the acid to Sb atom is III) was added to a solution of 5 parts antimony trioxide dissolved in 200 parts of ethylene glycol by heating and followed by the agitation over a period of 5 hours with the temperature being maintained at 120C. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg for 2 hours.

The resultant polymer had an intrinsic viscosity [1;] of 0.775 and a melting point of 261C and exhibited excellent luster and was extremely light with a very slight yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 89.4% and a PI value of 98.9% and exhibiting excellent luster and whiteness.

EXAMPLE 38 Using 10.3 parts of antimony acetate (Sb content of which corresponds to parts of Sb O in place of antimony trioxide and 5 parts of dimethylfumaric acid (a molar ratio of the acid to Sb atom is l/l in place of fumaric acid, a process of Example 37 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.772 and a melting point of 261C and was transparent with a very slight yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 89.4% and a PI value of 98.8% and exhibiting excellent luster and whiteness.

EXAMPLE 39 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate, while methanol, produced therefrom, was distilled off from the reaction mixture, to perform ester-interchange. The reaction was completed 3 hours after its initiation. Then, an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased. A solution of 3.2 parts trimethyl phosphate in ethylene glycol was then added to the reaction product at a temperature of 240C and followed by the addition of a catalytic antimony compound solution, prepared as follows; 4.45 parts of itaconic acid (a molar ratio of the acid to Sb atom is III) was added to a solution of 5 parts antimony trioxide dissolved in 200 parts of ethylene glycol by heating and followed by the agitation over a period of 5 hours with the temperature being maintained at a temperature of 120C. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg for 2 hours.

The resultant polymer had an intrinsic viscosity [1;] of 0.772 and a melting point of 260.5C and exhibited excellent luster and was extremely light with a very slight yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 87.5% and a P1 value of 98.8% and exhibiting excellent luster and whiteness.

EXAMPLE 40 A process of Example 39 was repeated under the same conditions as those in Example 39 except for added amounts of itaconic acid was 8.9 parts (a molar ratio of the acid to Sb atom is 2/1) in place of 4.45 parts.

The resultant polymer had an intrinsic viscosity [1 of 0.745 and a melting point of 260C and was tinged slightly yellow but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 86.0% and a PI value of 98.2% and exhibiting high lightness with a very slight yellow tinge.

EXAMPLE 41 Using 10.3 parts of antimony acetate (Sb content of which corresponds to 5 parts of Sb O in place of antimony trioxide and 4 parts of succinic acid (a molar ratio of the acid to Sb atom is 1/1 in place of itaconic acid, a process of Example 39 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1 of 0.766 and a melting point of 260C and was trans- 24 parent with a slight yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 86.4% and a PI value of 99.0% and exhibiting extreme lightness with a very slight yellow tinge.

EXAMPLE 42 Using 8.8 parts of antimony triethoxide in place of antimony trioxide and 5.9 parts of cyclohexane-l,2- dicarboxylic acid (a molar ratio of the acid to Sb atom is H1) in place of itaconic acid, a process of Example 39 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1 of 0.768 and a melting point of 261C and exhibited excellent whiteness with little or no yellow tinge. Filaments formed therefrom, were characterized as having a Y value of 87.8% and a PI value of 98.9% and exhibiting luster and whiteness.

EXAMPLE 43 A mixture of 9,000 parts dimethyl terephthalate, 1,000 parts of dimethyl isophthalate and 7,500 parts of ethylene glycol were heated at temperatures of to 220C for 3 hours in the presence of 5 parts of calcium acetate to perform ester-interchange. An excess of ethylene glycol was distilled off from the reaction product with the temperature being further increased. A solution of 2.3 parts trimethyl phosphate was added to the product at a temperature of 240C followed by the addition of a catalytic antimony compound solution, which was prepared by adding 3 parts of cyclobutane- 1,2-dicarboxylic acid (a molar ratio of the acid to Sb atom is l/l) to a solution of 6.2 parts of antimony acetate dissolved in 150 parts of ethylene glycol by heating. The resultant mixture was vacuumed by degrees with the temperature being increased and finally, poly-condensed at a temperature of 285C and a pressure of 2 mmHg for 2 hours.

The resultant polymer had an intrinsic viscosity [1;] of 0.686 and exhibited excellent whiteness and transparency. Filaments formed therefrom, were characterized as having a Y value of 89.1% and a PI value of 99.2%.

For comparison purposes, polycondensation, mentioned above, was repeated without using cyclobutane- 1,2-dicarboxylic acid. The resultant polymer was tinged with dark grey.

EXAMPLE 44 Using 4.5 parts of oxalacetic acid (a molar ratio of the acid to Sb atom is l/l) in place of itaconic acid, a process of Example 39 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [7 of 0.776 and a melting point of 260.5C and was clear with a very slight yellow tinge but little or no darkening. Filaments formed therefrom, were characterized as having a Y value of 87.7% and a PI value of 98.6% and excellent luster and whiteness.

EXAMPLE 45 Using 5.56 parts of ethoxysuccinic acid (a molar ratio of the acid to Sb atom is l/l in place of itaconic acid, a process of Example 39 was repeated with all other conditions remaining the same.

The resultant polymer had an intrinsic viscosity [1;] of 0.764 and a melting point of 261C and little or no =25 darkening. Filaments obtained therefrom, were characterized as having a Y value of 88.1% and a PI value of 98.8% and exhibiting excellent luster and whiteness.

EXAMPLE 46 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate, while methanol, produced therefrom, was continuously distilled off from the mixture, to perform ester-interchange. The reaction was completed 3 hours after its initiation. Then, an excess of ethylene glycol was distilled off from the reaction product with the temperature being increased. A solution of 3.2 parts trimethyl phosphate in ethylene glycol was then added to the reaction product at a temperature of 240C followed by the addition of 26 were characterized as having a Y value of 84.4% and a PI value of 99.0% and exhibiting excellent luster.

EXAMPLES 47 54 Using various compounds, which have the structure of at least one oxygen atom of the hydroxyl and the carboxyl groups in oz-hydroxycarboxylic acid being substituted with a sulfur atom, in place of malic acid,

Table 2 Used amounts of Examcom- Y Pl pound v V ple (A) 'M.P. value value No. Compound (A) (parts) [1 (C) s s)2CCOOH v 47 8.35 0.766 261 87.8 i 98.6

C H CHCOOH 48 5.75 0.75l 261 86.8 98.9

49 nococH,-C cooi-l 5.65 0.749 261 88.4 98.7

' HOCOCH CH CH-COOH HSCH CH-COOH 51 4.72 0.744 261 86.6 98.6

HOCOCH-CH-COOH 52 6.23 0.752 262 87.3 98.8

SH sn (HOCOCl-lmC-COOH 53 7.12 0.762 26l 88.7 98.7

54 HSCH COOH 3.15 0.742 260 85.8 98.8

a catalytic antimony compound solution, which was prepared as follows; 5.7 parts of phthalic acid (a molar ratio of the acid to Sb atom is III) was added at room temperature to a solutionof 5 parts antimony trioxide dissolved in 200 parts'of ethylene glycol by heating followed by agitation over a period of 5 hours with the temperature being maintained at 150C. The resultant mixture was vacuumed by degrees and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg for 2 hours.

The resultant polymer had an intrinsic viscosity [1;] of 0.772 and a meltingpoint of 261C and was tinged with a little darkening. Filaments obtained therefrom,

EXAMPLES 55 61 Using various compounds, which have the structure of at least one oxygen atom of the carboxyl group in a,B-dicarboxylic acid being substituted with a sulfur atom, in place of malic acid, processes of Example 1 were repeated with all other conditions remaining the same.

Results are shown in Table 3, from which it is apparent that all the inventive processes result in polymers having excellent transparency and whiteness with considerably reduced darkening with high productivity, in comparison with a conventional process wherein the most popular one among antimony catalysts, i.e. antimony trioxide, is used alone.

' Table 3 Used amounts Examcom- Y Pl pound ple (A) M.P. value value No. Compound(A) (parts) [11] (C) HOC H HCOSH H-COOH CH-COSH CH, COH

H COSH COSH coon

" CH -COSH C H HCOOH 60 7.19 0.751 260.5 87.3 98.3

i H=COSH N CH; HCOSH 61 6.10 0.755 261 86.8 98.7

CH HCOSH cut that all the inventive processes result in polymers EXAMPLES 62 71 having excellent transparency and whiteness with con- Using various derivatives of a-hydroxycarboxylic siderably reduced darkening with high productivity, in

acid in place of malic acid, processes of Example 1 comparison with a conventional process wherein the were repeated with all other conditions remaining the 35 most popular one among antimony catalysts, i.e. antisame. mony trioxide, is used alone.

Results are shown in Table 4, from WhlCh it IS appar- Table 4 Used amounts Exof comampound Y Pl ple (A) [1 M.P. value value No. Compound (A) (pans) (C) c m) coocH,cH,oH 62 9.3 0.753 260 88.3 98.7

HOCHCHZOCOCHZ H-COOCHCHOH 63 7.6 0.755 260 89.1 98.8

HOCH, H'COOCH2CHOH 64 5.|3 0.747 261 88.8 98.9

(C,H,0COCH,), C00C,H 65 6.48 0.740 261 87.9 98.7

CH5OCOCH2 H H--COOC2H5 66 7.55 0.744 260 88.0 98.8

(CGHSXC BH5CH2) CONH2 67 8.25 0.739 260 87.3 98.4

H (C t)2 2 68 7.77 0.742 260 87.7 98.8

CBH5 H-COOCOCH, 69 6.65 '0.749 261 88.1 98.7

8 C0Cl 70 8.6 0.742 261 87.3 98.8

Table 4-continued Used amounts Exof comampound Y Pl l 7 MP. value 'value No. Compound (A) (parts) ("C) ClCOCHCH-COCl 71 6.4 0.747 260 86.8 98.8

OH OH EXAMPLES 72 8O EXAMPLES 81 85 Using various derivatives of the compound, which compound has the structure of at least one oxygen atom of the hydroxyl and the carboxyl groupsin ahydroxycarboxylic acid being substituted with a sulfur atom(s), in place of malic acid, processes of Example 1 were repeated with all other conditions remaining the same.

Results are shown in Table 6, from which it is apparent that all the inventive processes result in polymers having excellent transparency and whiteness with considerably reduced darkening with high productivity, in comparison with a conventional process wherein the most popular oneamong antimony catalysts, i.e. antimony trioxide, is used alone.

Table 5 Used amounts Exof compound Y Pl ple (A) [1 M.P. value value No. Compound (A) (parts) (C) HCC0 72 O 3.36 0.746 26] 88.8 98.6

H-CCO CH,=CCO 73 O 3.84 0.747 26] 87.4 98.8

cH, co

C,H .,OCH-C0' 74 4.94 0.755 260 87.8 98.7

cn -co CH-COOCOCH 75 6.85 0.742 260 88.2 98.7

CH-COOCOCH HOCH CH OCOCH 76 5.48 0.743 260 87.4 98.6

CH.CO0H

COOCH CH OH 77 2 2 7.2 0.739 261 86.0 98.8

COOH

C,,H,---CCONH 78 9.l4 0.737 260 86.6 98.6

C H CCOOH CH,=C -COC| 79 5.72 0.744 261 86.9 98.8

CH COCI C.,H,,CHCOCI 80 8.ll 0.737 260 87.2 98.8

CH COCl Table 6 Used amounts Exofcomam pound Y P1 ple (A) [1;] MP. value value No. Compound (A) (parts) (C.)

(C6H5)2 COOCH,CH OH 81 9.87 0.747 261 87.8 98.5

CH OCCH HCOOCH CH OH 82 7.13 0.743 260 87.1 98.7

a COSC,,H 83 11.5 0.741 261 86.8 98.7

CH OCOCl-b H-CONH, 84 5.58 0.747 261 87.2 98.7

' CICOCH CH, H-COC1 85 6.88 0.743 261 88.0 98.7

EXAMPLES 86 91 mony compound solution, which was prepared by adding an organic acid to a solution of 5 parts antimony trioxide dissolved in 200 parts of ethylene glycol by heating followed by agitation with the temperature being maintained at 100C for 3 hours, and a cobalt compound were successively added to the reaction mixture. Results are shown in Table 8, from which it is apparent that use of both antimony and cobalt com- Table 7 Used amounts Exof comampound Y P1 P (A) [1 MP. value value No. Compound (A) (parts) (C) HCO 86 3.9 0.750 261 88.3 98.7

CH-CO CH CO 87 S 4.38 0.746 261 87.8 98.8

H CO

C H,,CHCO 88 6.44 0.750 261 87.1 98.9

cn -co C H SCO H 89 7.67 0.739 260 86.9 98.7

CHCOSH CH =C-COSCH CH,OCH 90 9.52 0.744 261 87.4 98.7

H,COSCH,CH OCH C1-1;,CCONH 91 L]: 5.45 0.740 261 86.6 98.6

CH 3 COSH Examples 92 96 Process of Example 1 were repeated under the same conditions as those in Example 1 except that an antipounds results in polymers having a higher Pl value, i.e. more improved whiteness without a yellow tinge.

Table 8 Organic acid and Cobalt compound Y Pl Ex. its used amounts and its used M.P. value value No. (parts) amounts (parts) [1;] (C) HOOCC1-1(OH)CH COOH Cobalt acetate 92 0.732 261 89.7 99.7

(C H COOH Cobalt acetate 93 0.745 261 88.7 99.8

H-COOH Cobalt acetate 94 0.746 261 89.8 100.0

CH-COOH 3.97 0.3

i-iococn H-COOH Cobalt acetate 95 0.743 261 88.7 99.5

Cobalt chloride 96 HOCH, COO1-1 0.742 261 88.8 99.7

' uct. Thereafter, the mixture was vacuumed b de rees EXAMPLE 97 y g 10,000 parts of dimethyl terephthalate and 7,500 parts of ethylene glycol were heated at temperatures of 150 to 220C under an atmosphere of nitrogen in the presence of 6 parts of magnesium acetate to effect ester-interchange while methanol, produced therefrom, was continuously distilled off from the reaction mixture. The reaction was completed three hours after its initiation. The reaction product was then distilled by heating to remove an excessof ethylene glycol therefrom. g

A solution of 3.2 parts of trimethyl phosphate in ethylene glycol was added at-atemperature of 240C to the reaction product.. Then, a solution of 5 parts of antimony trioxide in 200 parts of ethylene glycol and a solution of 4.6 parts of malic acid in 50'parts-of ethylene glycol were separately addedto the reaction prod-,

and finally, polycondensed at a temperature of 285C and a pressure of 2 mmHg over a period of 2 hours.

The resultant polymer had a melting point of 261C and an intrinsic viscosity [1 of 0.775. Thepolymer was transparent with a very slight yellow tinge but little or no darkening. Filaments, obtained therefrom bya normal spinning and drawing procedure, were characterized as having a Y value of 88.0% and a PI value of 98.7% and exhibiting excellent whiteness and luster.

EXAMPLES 98 i 13 The procedure as described=in Example. 97 was repeated except that the solution of 4.6 parts of malic .acid in ethylene glycol was replaced by a solution of Table9 Compound added Polymer Filaments Y P1 Ex. M.P. value value No. Structure (pans) [n] "(C) Y Hococii, COO1-l HOC l-l 1-1COO|-1 99 v 0.755 261 87.6 98.9

H-COOH 100 0.766 261 87.5 98.8

CH-COOH 4.0

CH CO01-1 101 1 4.45 0.769 260.5 87.7 98.8 H -COOH H-cog 102 3.36 0.748 261 88.6 98.8

ci-l-co HOCOCH; H-COOH 103 5.3 0.757 261 87.5 98.5

' C,,H H-COOl-1 (C H COOH 105 8.35 0.762 261 87.9 98.6

Table 9-continued Compound added Polymer Filaments Y Pl Ex. M.P. value value No. Structure (parts) 11;] (C) I COSH 106 (OOH 6.23 0.742 26| 85.7 98.3

H-CO 107 l S 3.9 0.755 261 88.1 98.7

CHCO

C,H O-CHCOOH I08 6.10 0.745 260.5 87.3 98.6

CH COSH (C,H C-COOCH CH,OH 109 9.3 0.755 261 88.3 98.6

HOCH CH,OCO-CH CH-COOCH,CH OH 110 0.757 260.5 89.3 98.8

C H CHCOOCOCH, 111 6.65 0.744 260 88.0 98.5

cH,=c c'oc1' 112- 5.72 0.747 261 86.6 98.3 1 c11 c oc1 w cmo'cocmen-c0801 1 13 5.58 -0.749' 260 87.1 98.5

EXAMPLE 114 The procedure as described in Example 97 was repeated except that the parts of antimony trioxide was replaced by 8.8 parts of antimony triethoxide.

. The resulting polymer was clear and transparent, having an intrinsic viscosity [1 of 0.772 and a melting .pointrof 261 C. Filaments obtained therefrom were characterized as having a Y value of 87.4% and a PI value of- 98.9% and exhibiting excellent whiteness and luster.

EXAMPLE 1 Filaments obtained therefrom were,characterized as having a Y value .of 89.4%.and a PI value of 99.1% and exhibiting excellent. whiteness and luster.

I EXAMPLE' I l6 EXAMPLES ll7 127 The procedure of Example 1 16 was repeated except that the 4.6 parts of solid malic acid was replaced by each of the compounds indicated in Table 10. The results are also shown in the same table.

Table I0 Compounds added Polymer Filament;I

Y Ex. M.P. value value No. Structure (par ["7] (HOCOCH:) CCO0H ll7 I 0.759 26! 88.5 98.1

H--COOH V I18 I 4.0 0.762 260 87.5 98.5

H-COOH CH =CCO0H I I9 4.45 0.766 261 87.9 98.4

CH COOH HOCOCH, H-COOH I20 SH 5.3 0.760 26] 87.5 98.0

Table lO-continued Compounds added Polymer Filament;I

. Y Ex. M.P. value value No. Structure (parts) [1 (C) CH5CHCOOH 121 5.75 0.755 260 86.5 98.2

cosn

COOH I CHCO\ 123 H s 3.9 0.750 261 87.6 98.3

CH-CO f (c,,11,),c-coocn c11 0 Y 124 9.3 0.755 260 88.1 98.5

H0CH CH,OCOCH CHCOOCH,CH,0H 125 0.751 260 88.4 98.1

CH,=CCOC1 126 1 5.72 0.743 261 86.3 98.1

CH,-COC I "cn,ococ1-1,cu coNn, 127 5.58 0.744 261 86.9 98.8

What we claim is: 1. A process for preparing linear polyesters compris- 2/ COOH mg condensing glycol terephthalate by incorporating into the polycondensation system an antimonycontain- R 3\ ing polycondensation catalyst which is soluble in the R /C COOH /C COOH polycondensation system and at least one member selected from the group consisting of (l) a-hydroxycar- R3 boxyhc ac1d hav1ng 2- to 30 carbon atoms: (2) a,B- 1 A] dicarboxylic acid having 4 to 30 carbon atoms; and COOH C COOH (3ester, amide, acid anhydride, mixed acid anhydride a \"/c -coo11 or acid halide, of said a,B-dicarboxylic acid; R2 L I 2. A process according to claim 1, wherein said ahydroxycarboxylic acid having 2 to 30 carbon atoms w has a total of at least three hydro cyl and carboxyl Rl C COOH X coo" groups or has at leastone aromat1c ring in the a-position in relation to the carboxyl group. -R,- --COOH Y COOH 3. A process according to claim-1, wherein said a- 1 hydroxycarboxylic acid is tartaric acid, a-methyltartaric acid, citric acid, malic acid, a-methylmalic acid, trimethylmalic acid, a-hydroxya'-methylsuccinic acid, a-hydroxy-a, a-dimethylsuccinic acid, a-hydroxyglutaric acid, glyceric acid, 4-hydroxypentane-l,3,4 tricarboxylic acid, afi-dihydroxyisobutyric acid, 01,3- dihydroxyglutaric acid, dihydroxyfumaric acid, gluconic acid, 2,3,4-trihydroxybutyric acid, tartronic acid, methyltartronic acid, benzilic acid or a-phenyllactic acid.

4. A process according to claim 1, wherein said ahydroxycarboxylic acid is glycollic acid, a-hydroxystearic acid, a-hydroxyvaleric acid, a-hydroxyisobutyric acid or a-hydroxyauric acid.

5. A process according to claim 1, wherein said 02,3- dicarboxylic acid having 4 to 30 carbon atoms is a member selected from the group consisting of the compounds represented by the following formulae:

wherein R R R and R are identical with or different from each other and are hydrogen atom or unsubstituted or substituted alkyl, cycloalkyl, aryl, aralkyl, allyl or alkoxyl group, said substituted groups having a substituent selected from carbonyl group, halogen and carboxyl group; W, X, Y and Z are identical with or different from each other and are hydrogen atom or alkyl, hydroxyl or carboxyl group; and n is an integer of at least I.

6. A process according to claim 1, wherein said oz,fi-- dicarboxylic acid is maleic acid, fumaric acid, succinic acid, methylsuccinic acid, a-ethoxysuccinic acid, 2,3- dimethylsuccinic acid, itaconic acid, cyclohexaned ,2- dicarboxylic acid, l-phenylcyclopropane-2,3-dicarboxylic acid, cyclobutane-l ,2-dicarboxylic acid, cyclopentane-l ,2-dicarboxylic acid, cyclohexane-l,2-dicarboxylic acid, oxalacetic acid, phthalic acid, cyclobu- 

1. A PROCESS FOR PREPARING LINEAR POLYESTERS COMPRISING CONDENSING GLYCOL TEREPHTHALATE BY INCORPORATING INTO THE POLYCONDENSATION SYSTEM AN ANTIMONYCONTAINING POLYCONDENSATION CATALYST WHICH IS SOLUBLE IN THE POLYCONDENSATION SYSTEM AND AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF (1) A-HYDROXYCARBOXYLIC ACID HAVING 2 TO 30 CARBON ATOMS (2) A,B-DICARBOCYLIX ACID HAVING 4 TO 30 CARBON ATOMS; AND (3ESTER, AMIDE, ACID ANHYDRIDE, MIXED ACID ANHYDRIDE OR ACID HALIDE, OF SAID A,B-DICARBOXYLIC ACID;
 2. A process according to claim 1, wherein said Alpha -hydroxycarboxylic acid having 2 to 30 carbon atoms has a total of at least three hydroxyl and carboxyl groups or has at least one aromatic ring in the Alpha -position in relation to the carboxyl group.
 3. A process according to claim 1, wherein said Alpha -hydroxycarboxylic acid is tartaric acid, Alpha -methyltartaric acid, citric acid, malic acid, Alpha -methylmalic acid, trimethylmalic acid, Alpha -hydroxy- Alpha ''-methylsuccinic acid, Alpha -hydroxy- Alpha , Alpha ''-dimethylsuccinic acid, Alpha -hydroxyglutaric acid, glyceric acid, 4-hydroxypentane-1,3, 4-tricarboxylic acid, Alpha , Beta -dihydroxyisobutyric acid, Alpha , Beta -dihydroxyglutaric acid, dihydroxyfumaric acid, gluconic acid, 2,3,4-trihydroxybutyric acid, tartronic acid, methyltartronic acid, benzilic acid or Alpha -phenyllactic acid.
 4. A process according to claim 1, wherein said Alpha -hydroxycarboxylic acid iS glycollic acid, Alpha -hydroxystearic acid, Alpha -hydroxyvaleric acid, Alpha -hydroxyisobutyric acid or Alpha -hydroxyauric acid.
 5. A process according to claim 1, wherein said Alpha , Beta -dicarboxylic acid having 4 to 30 carbon atoms is a member selected from the group consisting of the compounds represented by the following formulae:
 6. A process according to claim 1, wherein said Alpha , Beta -dicarboxylic acid is maleic acid, fumaric acid, succinic acid, methylsuccinic acid, Alpha -ethoxysuccinic acid, 2,3-dimethylsuccinic acid, itaconic acid, cyclohexane-1,2-dicarboxylic acid, 1-phenylcyclopropane-2,3-dicarboxylic acid, cyclobutane-1,2-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid, cyclohexane-1,2-dicarboxylic acid, oxalacetic acid, phthalic acid, cyclobutane-1,2-dicarboxylic acid or 1-butene-2,3, 4-tricarboxylic acid.
 7. A process according to claim 1, wherein said antimonycontaining polycondensation catalyst is at least one member selected from antimony trioxide, antimony halide, antimony sulfide, antimonic acid and metal salt thereof, antimonous acid and metal salt thereof, antimony glycoxide, antimony phenoxide, antimony alkoxide and antimony carboxylate.
 8. A process according to claim 1, wherein from 0.005 to 0.5% by weight of said antomonycontaining polycondensation catalyst, based on the weight of the resulting polyester, is incorporated into the polycondensation system.
 9. A process according to claim 1, wherein said member selected from the group consisting of said Alpha -hydroxycarboxylic acid acid, said Alpha , Beta -dicarboxylic acid, and said ester, amide, acid anhydride, mixed acid anhydride or acid halide thereof of said Alpha , Beta -dicarboxylic acid, is incorporated into the polycondensation system in an amount such that the molar ratio of the antimony atom contained in said polycondensation catalyst to said member unit falls within the range from 1: 0.5 to 1:
 3. 10. A process according to claim 9, wherein said molar proportion of antimony atom contained in said polycondensation catalyst to said member unit is 1 :
 1. 11. A process according to claim 1, wherein at least one catalytic metal compound selected from soluble germanium, titanium, tin, lead, zinc and cobalt compounds is present in addition to said antimony-containing polycondensation catalyst.
 12. A process according to claim 11, wherein said germanium compound is amorphous or crystal germanium dioxide, an eutectic mixture of crystal germanium dioxide and antimony trioxide, germanium alkoxide, germanium carboxylate or germanium tetrahalide and is used in the form of solid, an aqueous solution, an ethylene glycol solution being prepared by replacing the medium of the aqueous solution by ethylene glycol or by directly dissolving the germanium compound in ethylene glycol in the presence of alkali metal salt or alkaline earth metal salt.
 13. A process according to claim 11, wherein said cobalt compound is a carboxylic acid salt such as cobalt formate, cobalt acetate, cobalt benzoate and cobalt stearate, acetyl-acetonatocobalt, cobalt chloride, cobalt bromide, cobalt nitrate or cobalt sulfate.
 14. A process according to claim 1, wherein said glycol terephthalate is ethylene glycol terephthalate, 1,4-butanediol terephthalate or 1,4-cyclohexanedimethanol terephthalate.
 15. A process according to claim 1, wherein said antimony-containing polycondensation catalyst and said member selected from the group consisting of the Alpha -hydroxycarboxylic acid, Alpha , Beta -dicarboxylic acid and the ester, amide, acid anhydride, mixed acid anhydride or acid halide of the Alpha , Beta -dicarboxylic acid are incorporated into the polycondensation systems as they are.
 16. A process according to claim 1, wherein said antimony-containing polycondensation catalyst and said member selected from the group consisting of the Alpha -hydroxycarboxylic acid, Alpha , Beta -dicarboxylic acid and the ester, amide, acid anhydride, mixed acid anhydride or acid halide of the Alpha , Beta -dicarboxylic acid are incorporated into the polycondensation system, in the form of either separate solutions or a common solution in glycol.
 17. A process according to claim 16, wherein said glycol is ethylene glycol, propylene glycol, 1,4-butanediol or 1,4-cyclohexanedimethanol.
 18. A process for preparing linear polyesters comprising condensing glycol terephthalate by incorporating into the polycondensation system an antimonycontaining polycondensation catalyst selected from the group consisting of antimony trioxide, antimony triethoxide, antimony acetate and antimony glycoxide, and at least one member selected from the group consisting of tartaric acid, Alpha -methyl tartaric acid, citric acid, malic acid, Alpha -methylmalic acid, Alpha -hydroxy- Alpha ''-methylsuccinic acid, Alpha -hydroxyglutaric acid, glyceric acid, Alpha , Beta -dihydroxyisobutyric acid, dihydroxyfumaric acid, gluconic acid, tartronic acid, methyltartronic acid, benzilic acid, Alpha -phenyllactic acid, glycollic acid, Alpha -hydroxystearic acid, Alpha -hydroxyisobutyric acid, trimethylmalic acid, Alpha -hydroxy- Alpha , Alpha '' -dimethylsuccinic acid, 4-hydroxypentane-1,3,4-tricarboxylic acid, Alpha , Beta -dihydroxyglutaric acid, 2,3,4-trihydroxybutyric acid; maleic acid, fumaric acid, succinic acid, Alpha -ethoxysuccinic acid, itaconic acid, cyclohexane-1,2-dicarboxylic acid, oxalacetic acid, phthalic acid, cyclobutane-1,2-dicarboxylic acid,1-butene-2, 3,4-tricarboxylic acid, methylsuccinic acid, 2,3-dimethylsuccinic acid, itaconic acid, 1-phenylcyclopropane-2,3-dicarboxylic acid, cyclopentane-1,2-dicarboxylic acid; and ester, amide, acid anhydride, mixed acid anhydride or acid halide, of the above-listed Alpha , Beta -dicarboxylic acids. 